Habitat quality and the impact of natural enemies might profoundly affect
metapopulation dynamics and viability. However, their relative impact has usually been
considered independently. Here we address the question of how caterpillar habitat quality
and parasitism prevalence interact to shape habitat selection in the bog fritillary butterfly
Boloria eunomia, parasitized at the caterpillar stage by a specialist wasp, Cotesia euno-
miae. We first classified habitat quality by relating caterpillar density to descriptors of
different microhabitat types. Second, we investigated parasitism prevalence in those dif-
ferent microhabitats. Our results show that caterpillars and parasitoids mapped onto the
same microhabitats, mainly zones with high abundance of the host plant. Accordingly, we
suggest that both egg-laying females and parasitoids use the same cues for habitat selec-
tion. As a consequence, there should be a fitness cost for B. eunomia females to lay their
eggs in places where parasitism prevalence is high. We indeed detected that B. eunomia
females frequently laid eggs in habitat types that presented suboptimal microhabitat
conditions for caterpillars. This suggests that the lower parasitism prevalence in these
suboptimal habitat types counterbalances lower caterpillar survival, leading to an overall
similar survival in optimal and suboptimal habitat types. Spreading eggs in different
habitat types is thus expected to be a safe strategy to mitigate the adverse possible effects
of environmental stochasticity and parasitism prevalence on offspring survival unequal
among microhabitat types. From a conservation viewpoint, the preservation of habitat
heterogeneity, including optimal but also suboptimal habitat areas, is crucial to ensure
persistence of both the host and its parasitoid.